A broad range of electrical conductors and electrical cables are installed in modern buildings for a wide variety of uses. Some of these uses are data transmission for computer systems, voice communications, as well as control signal transmission for building security, fire alarm, and environmental control systems. Some of these cables networks are frequently installed in the through-space between the dropped ceiling and floor above, currently referred to as the Plenum area. Electrical conductors and cables extending through plenum areas are governed by special provisions of the National Electric Code (“NEC”).
The National Fire Protection Association (“NFPA”) recognized the potential flame and smoke hazards created by burning cables in Plenum areas and adopted in the NEC a standard for flame retardant and smoke suppressed cables. This standard permits the use of cable without conduit, so long as the cable exhibits low smoke and flame retardant characteristics.
The test method used for such distinctions is the Steiner Tunnel flame test. This method has been adopted as NFPA 262 and Underwriters Laboratory (UL) 910. The test conditions for are as follows: a 300,000 BTU/hour flame is applied for 20 minutes to a tray of cable, which is 1 foot wide by 24 feet long, mounted horizontal within the Steiner Tunnel. The criteria for passing the flame test is a maximum flame spread of five feet, a maximum optical density of smoke less than or equal to 0.50, and an average optical density of smoke of less or equal to than 0.15.
The most commonly used telecommunication cable has four unshielded twisted pairs of insulated conductors (4 UTP). A majority of these cables use fluorinated ethylene/propylene polymers (FEP) as the insulation material of choice with a low smoke polyvinyl chloride jacket. The advantages of FEP are excellent electrical properties with a high degree of flame retardancy. However, FEP has many disadvantages as well. FEP is very expensive and drips off of the cable when exposed to a flame. This hot molten polymer also will release a very aggressive acid gas in hydrofluoric acid (HF). This gas is extremely toxic to humans when they are even exposed to small amounts.
An insulation material or combination of materials that could pass all the electrical and smoke requirements of NFPA 262, while not dripping off the cable when exposed to a flame, be low toxic and low corrosivity, and come at a lower cost would be useful in this application. This need has been established by industry trends of replacing some of the FEP with an alternate cheaper material. Until this time there has not been an insulation composition that was able to fully replace the FEP insulation in the telecommunications cable.
The present invention details polymeric compositions that can fully or partially replace FEP insulation while not dripping off the cable when exposed to a flame, with toxicity and corrosivity and comes at a much lower cost.